For a variety of machines that carry out reciprocal, rotary movements, and the like, sliding members are indispensable generally. For example, various sliding members have been utilized in engines, compressors, and so forth, as well.
In general, in sliding surfaces, it is desirable that the sliding surfaces can turn into a mirror surface in order to decrease the wear amount by friction. However, when a sliding surface turns into a mirror surface, although the friction resistance between metals, which are subjected to a mirror-surface finishing, can be suppressed when they are rubbed to each other by way of oil, there might be a fear of seizure because a certain amount of heat generates. Accordingly, for sliding surfaces, in order to meet their respective applications, those with appropriate surface roughness being provided, and those whose superficial sliding characteristics are modified by performing a surface treatment, such as plating, onto the sliding surface have been required.
Moreover, it has been carried out generally to supply an adequate lubricating agent between sliding surfaces, thereby diminishing the frictional force and wear or superficial damages of other forms. In order to secure a sufficient oil-film thickness, it is needed to retain the lubricating agent in an adequate amount on the sliding surfaces. In order to secure the lubricating agent in an adequate amount, such a technique has been carried out since long time ago that “X”-shaped streaklike marks, so-called cross-hatchings, for instance, are made in sliding surfaces so as to retain the lubricating agent within the streaklike marks.
An iron-based sliding material is set forth in Patent Literature No. 1, iron-based sliding material which comprises 5-50% by weight TiCN and the balance of an iron-based alloy; whose porosity is adapted into being 7-20% by volume in a superficial portion from a surface of the sliding surface to a depth of 1 mm; and whose internal porosity is decreased less than this. The fact that, when the iron-based sliding member set forth in Patent Literature No. 1 is used under such a condition that a lubricating oil exists, the frictional wear can be improved considerably is disclosed therein, because the pores in the superficial portion are impregnated with the lubricating oil.
An iron-based sintered alloy is set forth in Patent Literature No. 2, iron-based sintered alloy which comprises: a dispersion phase of at least one or more members of oxides, carbides and sulfides of Ca, Sr and Ba, and mutual solid solutions of these, or carbon, in a sintered alloy; a hard phase of at least one member of carbides and nitrides of metals of groups 4a, 5a and 6a in the periodic table, and mutual solid solutions of these; and the balance of a binder phase comprising an alloy that includes ferrite, austenite, martensite or Fe as a major component; in which the dispersion phase is removed from a superficial portion of the iron-based sintered alloy so that fine pores are formed. The following is disclosed: in the iron-based sintered alloy set forth in Patent Literature No. 2, it is possible to impregnate the inside of the fine pores that are formed in the superficial portion with a lubricating substance, thereby lowering the friction coefficient.
In Patent Literature No. 3, performing a shot peening treatment onto a sliding surface of sliding member (quality of material: carbon steel, chromium steel, or chromium-molybdenum steel) using shots with 0.6-1.0 mm particle diameters is disclosed, thereby changing a superficial form of the sliding surface so as to reduce the friction coefficient at an initial stage of sliding (so as to turn the leading end of after-shotting superficial configuration into a rounded convex configuration). The following is also disclosed: it is possible to suppress the frictional heat generation by means of reducing the friction coefficient at an initial stage of sliding, and thereby it is possible to suppress the deterioration of lubricating grease.
Moreover, a few methods of modifying surfaces by means of shot blasting have been studied depending on their objectives, because it is possible to carry out processing even after sliding materials are formed into sliding members, and because it is possible to give them residual stresses by means of compression.
For example, in Patent Literature No. 4, there is disclosed, in order to control the wear of mating material in sliding, a method of removing edges, which arise from burrs and the like in polished surfaces, (rounding them, scraping them off, or cutting off the leading-end portions) by means of performing a shot jetting treatment onto a polished surface of mechanical component part in which hard particles, such as metallic carbide, are dispersed in large amount, polished surface to which a surface polishing treatment has been carried out. The following is also disclosed: it is possible to effectively suppress the wear of mating member upon sliding by means of removing the edges.
Moreover, in Patent Literature No. 5, there is disclosed a sliding member that is made from a powdery aluminum alloy, sliding member which is made from a powdery aluminum alloy in which iron-based hard particles and hard particles, that is, one member or more of ceramic particles whose hardness is lower than that of alumina, are dispersed, and powdery aluminum alloy which includes silicon, manganese and magnesium; sliding member in which a large number of concaved portions are formed in a sliding surface of the sliding member by means of shot blasting using fine particles with one of nickel and tin being coated; and additionally sliding member on which one of nickel coating and tin coating is formed. The following are also disclosed: the large number of concaved portions fulfill a role of oil reservoirs, thereby it is possible to secure an oil-retaining function for the sliding surface; and moreover nickel or tin coating is made on a surface of aluminum alloy that is likely to undergo agglomeration, and thereby it becomes less likely to wear so that it is possible to improve the scuff preventiveness; and the sliding surface undergoes work hardening by means of hitting the fine particles onto the sliding surface so that the wear resistance improves to that extent.
Patent Literature No. 1: Japanese Examined Patent Publication (KOKOKU) Gazette No. 63-1,383;
Patent Literature No. 2: Japanese Unexamined Patent Publication (KOKAI) Gazette No. 6-279,959;
Patent Literature No. 3: Japanese Unexamined Patent Publication (KOKAI) Gazette No. 9-268,319;
Patent Literature No. 4: Japanese Unexamined Patent Publication (KOKAI) Gazette No. 11-207,622; and
Patent Literature No. 5: Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2003-13,163